DTaP vaccine: What you need to know. Centers for Disease Control and Prevention website. Available at:
http://www.cdc.gov/vaccines/hcp/vis/vis-statements/dtap.pdf. Updated May 17, 2007. Accessed June 23, 2015.

Immunization schedules for infants and children. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/vaccines/schedules/easy-to-read/child.html. Updated January 26, 2015. Accessed June 23, 2015.